While the use of immunosuppression is crucial to the success of solid organ transplantation, it also predisposes patients to an increased incidence of infection and malignancy. Epstein Barr virus (EBV) B cell lymphomas associated with post-transplant lymphoproliferative disorder (PTLD) represent one of the most challenging, and serious, complications in transplant recipients. Currently, there is no consensus on treatment strategies for patients with PTLD, in part because the approaches utilized vary in their efficacy and because we cannot predict which therapy will best benefit a given patient. Furthermore, relapse and treatment-related mortality are major concerns. Our laboratory has worked to elucidate the underlying pathogenesis of EBV+ PTLD as a strategy to identify novel therapeutic targets. We have discovered that the PI3K/Akt/mTOR pathway is constitutively active in EBV+ B cell lymphomas from patients with PTLD and that EBV contributes to dysregulation of this pathway. We have also shown that survival and proliferation of EBV+ B cell lymphomas depends upon the PI3K/Akt/mTOR pathway because small molecule inhibitors, or siRNA, that target pathway constituents significantly inhibit lymphoma growth. In this proposal we plan to 1) determine the role of the PI3K/Akt/mTOR pathway in survival and growth of EBV+ B cell lymphomas, and identify rational therapeutics for targeting key nodes in the pathway; 2) determine whether targeting the PI3K/Akt/mTOR pathway affects the immune response to organ allografts and to EBV. To accomplish Aim 1 we will perform biochemical, molecular, cellular, and pharmacologic analysis of PTLD tissue and B cell lymphoma lines to identify sensitive nodes within the PI3K/Akt/mTOR pathway. We will also investigate the role of the viral oncogene, latent membrane protein 1, and host cell microRNA in the underlying dysregulation of the pathway. In Aim 2 we will utilize a murine heterotopic heart allograft model to determine the effect of PI3K/Akt/mTOR pathway modulation on the immune responses to an allograft. Finally, we will utilize mass cytometry to determine how PI3K/Akt/mTOR signal transduction contributes to alloantigen-specific and EBV-specific human T cell responses. These studies will create new opportunities for improving the treatment of EBV+ PTLD, and will also increase our basic understanding of EBV+ B cell lymphoma biology, allograft rejection, and alloantigen- and EBV-specific human T cell responses.